POSIX teaser

Last reviewed Jun 1, 2026 Content v20260601

Track mode: server_compiled
Means: Compiled runner
Reading: ~1 min
Level: advanced

This lesson

This lesson teaches POSIX teaser: the syntax, patterns, and safety habits you need before advancing in C.

Teams still ship POSIX teaser in C codebases—skipping it leaves gaps in debugging and code reviews.

You will apply POSIX teaser in contexts like: Linux daemons, shell utilities, and libc wrappers on Unix-like systems.

Write C in main.c with int main(), click Run on server—the dev runner compiles with cc/gcc -std=c11 and runs the binary; read stderr for compile and linker errors (LEARNING_RUNNER_ENABLED=true).

When pointers, structs, and basic control flow from intermediate lessons are familiar.

POSIX defines a portable Unix API: files, processes, pipes, sockets, and threads. C plus POSIX powers most Linux/macOS systems software.

Common POSIX calls

open, read, write, close — file descriptors
fork, exec, wait — processes
pthread_create — threads (pthread library)
socket — networking

stdio vs POSIX I/O

FILE* buffering is convenient; file descriptors integrate with select/poll and pipes.

Important interview questions and answers

Q: POSIX vs C standard?
A: C standard is language + libc basics; POSIX adds OS services beyond ISO C.
Q: fork() does what?
A: Creates a child process copying the address space—classic Unix process model.

Self-check

Name one POSIX call not in ISO C.
What is a file descriptor?

Interview prep

POSIX vs ISO C?: ISO C defines language and core libc; POSIX adds Unix OS APIs—processes, fds, pthreads, sockets.
fork()?: Creates child process duplicating parent memory image—cornerstone of Unix process model.

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Self-reflection (saved on this device)

Not saved yet.

Playground

Runs on the configured server runner (dev: npm run runner with LEARNING_RUNNER_ENABLED=true). Output appears below the editor.

Code runner not available

Server runner is disabled. Set LEARNING_RUNNER_ENABLED=true and LEARNING_RUNNER_URL in .env (see .env.example).

Check yourself

Multiple choice — immediate feedback.

Discussion

Past discussion is visible to everyone. Only logged-in users can post comments and replies.

Starter discussion topics

unistd.h for?
fork scary why?

No discussion yet. Be the first to ask a question.